A conventional Class D output stage as, for instance, M. Berkhout discloses in “An Integrated 200 W Class-D Audio Amplifier”, IEEE Journal of Solid-State Circuits, Vol. 38, No. 7, pp. 1198-1206, July 2003 may comprise a differential first operational amplifier as a feedback integrator at the input and a second operational amplifier as a trans-conductance amplifier as a second stage. The first operational amplifier constitutes a low impedance output stage configured to drive a feedback capacitor. The first operational amplifier compares a differential input signal with the output signal of the entire circuit and integrates a resulting error signal which is further integrated by the second operational amplifier.
The conventional Class D output stage may further comprise feed-forward analog adder stages following the second operational amplifier and securing stability. The adder stages add the output signals of the first and second operational amplifiers. Comparators following the adder stages compare the output signals of the adder stages with, for instance, a triangular wave form and drive power output stages.